Required Practical --> Photosynthesis

• What additional concept should higher tier students explain?

  How results are affected by the inverse square law
• What is the first step in the required practical for investigating photosynthesis?

  • Take a boiling tube
  • Place it 10 cm from an LED light source
• Why is an LED light used in the experiment?

  It doesn't release much heat
• What should you do if using a normal light bulb?

  Place a beaker of water between the light and tube
• What does sodium hydrogen carbonate solution release?

  Carbon dioxide
• What is the purpose of placing pond weed in the boiling tube?

  To observe oxygen production during photosynthesis
• How long should the pond weed acclimatize in the boiling tube?

  Five minutes
• What do you count to measure the rate of photosynthesis?

  The number of bubbles produced in one minute
• What should you do after counting bubbles for one minute?

  Repeat the count two more times
• What distances should you test in the experiment?

  10 cm, 20 cm, 30 cm, 40 cm
• What are the two main problems with counting bubbles?

  • Bubbles can be too fast to count accurately
  • Bubbles vary in size
• How can you solve the problem of counting bubbles?

  Measure the volume of oxygen produced
• What equipment is used to measure the volume of oxygen?

  A measuring cylinder filled with water
• What graph is plotted in the experiment?

  • Mean number of bubbles per minute
  • Volume of oxygen per minute
  • Against distance from the light source
• What happens to the number of bubbles per minute when the distance is doubled?

  It falls by a factor of four
• What is the scientific term for the relationship observed in the experiment?

  The inverse square law
• Why does light intensity affect the rate of photosynthesis?

  Light is needed for photosynthesis
• What should higher tier students be able to explain regarding the experiment?

  • How results are affected by the inverse square law